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Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framew
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets |
Date: |
Wed, 16 Jun 2010 16:07:14 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Jamie Lokier wrote:
> Anthony Liguori wrote:
> > On 06/16/2010 09:29 AM, Paolo Bonzini wrote:
> > >On 06/16/2010 04:22 PM, Jamie Lokier wrote:
> > >>Paolo Bonzini wrote:
> > >>>These should be (at least for now) block-obj-$(CONFIG_POSIX).
> > >>>
> > >>>>+ while (QTAILQ_EMPTY(&(queue->request_list))&&
> > >>>>+ (ret != ETIMEDOUT)) {
> > >>>>+ ret = qemu_cond_timedwait(&(queue->cond),
> > >>>>+ &(queue->lock), 10*100000);
> > >>>>+ }
> > >>>
> > >>>Using qemu_cond_timedwait is a hack for not properly broadcasting the
> > >>>condvar in flush_threadlet_queue.
> > >>
> > >>Are you sure? It looks like it also expires idle threads after a
> > >>fixed amount of idle time.
> > >
> > >Unnecessary idle threads are immediately expired as soon as the
> > >threadlet exits if ncecessary, since here
> >
> > If a threadlet is waiting to consume more work, unless we do a
> > pthread_cancel (I dislike cancellation) it will keep waiting until it
> > gets more work (which would mean it's not actually idle)...
>
> There's some mild abuse of the mutex/condvar going on.
>
> As (queue->exit || queue->idle_threads > queue->min_threads) is a
> condition for breaking out of the loop, that condition ought to be
> checked in the mutex->cond_wait region, but it isn't.
>
> It doesn't matter here because the queue is empty when queue->exit,
> and the idle > min_threads condition can't become true.
Sorry, thinko. It does matter when queue->exit, precisely because the
queue is empty :-)
Even cond_broadcast after queue->exit is set isn't enough to remove
the need for the timed wait hack.
Putting the whole condition inside the mutex->cond_wait region, not
just empty queue test, will remove the need for timed wait. Broadcast
is still needed, or alternatively a cond_signal from each exiting
thread will allow them to wake and close without a thundering herd.
-- Jamie
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, (continued)
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Paolo Bonzini, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Anthony Liguori, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Paolo Bonzini, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Anthony Liguori, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Corentin Chary, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Anthony Liguori, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Corentin Chary, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Gautham R Shenoy, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Gautham R Shenoy, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Jamie Lokier, 2010/06/16
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets,
Jamie Lokier <=
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Paolo Bonzini, 2010/06/16
- [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Gautham R Shenoy, 2010/06/17
- [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Paolo Bonzini, 2010/06/17
- Re: [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Anthony Liguori, 2010/06/17
- [Qemu-devel] Re: [PATCH V4 2/3] qemu: Generic task offloading framework: threadlets, Paolo Bonzini, 2010/06/18
[Qemu-devel] [PATCH V4 3/3] qemu: Convert AIO code to use threadlets., Gautham R Shenoy, 2010/06/16
Re: [Qemu-devel] [PATCH V4 0/3] qemu: Threadlets: A generic task offloading framework, Anthony Liguori, 2010/06/16